The specific aims of this research proposal are to identify the cis-acting regulatory elements and upstream transcription factors that control the expression of the basic helix-loop-helix (bHLH) transcription factors neurogenin 1 (ngn1) and neurogenin 2 (ngn2), which participate in the cascade of signals required for the differentiation of neural precursors during the development of the mammalian nervous system. Functional cis-acting regulatory elements will be identified from the ngn1/2 gene sequences using transgenic mouse assays and the nucleotide sequence analysis of several orthologs. The final goal of these experiments is to identify small domains flanking ngn1/2 that are sufficient to drive the expression of the lacZ reporter gene to defined regions of the spinal neural tube. Yeast one-hybrid screens with these minimal elements will be performed to identify upstream regulatory proteins that mediate the expression of ngn1/2. The regulation of ngn1/2 will also be studied using BAC transgenes. The long term objective of these studies is to better understand the regulation of the neural specific members of the diverse family of bHLH transcription factors and provide clues towards understanding the transition from a proliferating neural precursor to a post-mitotic differentiating neuron.